1. Field of the Invention
The present invention relates to an image forming method using an electrophotographic copying system.
2. Description of the Related Art
The object of an image forming apparatus such as a copying machine is to faithfully reproduce the image of an original document on a copy sheet.
The amount of a toner which is transferred to an electrostatic latent image formed on a photoreceptor drum is not proportional to an image density beyond a certain point. Therefore, when an original document having a photograph is copied, the tone of the image of the photograph is not preferable. In other words, the photograph of the original document cannot always be copied faithfully.
Japanese Laid-Open Patent Publication No. 43669/1985 discloses an image forming apparatus in order to solve this problem. According to this method, the image of letters are copied in the document-copying mode and that of a photograph is copied in a photograph-copying mode by adjusting the electric potential on the surface of an electrostatic latent image-holding member and the amount of a light applied to the letters and the photograph. Nevertheless, a part of the image of the photograph cannot be copied faithfully. Therefore, it is necessary to provide the image forming apparatus with a specific unit to correct such a defect.